Heuglin's Gull (L. heuglini / antelius)

(last update: 26-2-2014)

White underside of the base of P10 in heuglini.

Buzun (in British Birds, 2002) described the underside of the base of P10 for heuglini as being (pure) white in most birds, so not showing contrast with underwing coverts. Normally, Dutch graellsii have the base of the underside of P10 grey, silvery or pale greyish coloured. Buzun estimated 70-75% of heuglini in Russia to have white bases to P10 while only 1-3 % of Dutch birds (estimations based on photographs and our field data at Moerdijk) have white.

The problem to determine the exact grey-tone on the underside of P10 is exacerbated by the shiny, reflecting structure of the feather, making grey-tone change depending on observation angle. Thus, strict classification of the tone is debatable, as the appearance varies according to light conditions and relative angle of observation (e.g. commonly found in Dutch birds are 'silvery grey' bases of the underwing of P10, but this is still not pure white).

The Gull-Research Organisation has brought together a large group of internet images of adult heuglini on the wintering grounds (most of them photographed by Amir Ben Dov in Israel) and birds in N Europe (assumed to be heuglini in Finland, photographed by Hannu Koskinen). Despite the birds photographed in the field and not in the hand, these images contradict the view of Buzun, that 70-75% show a white base on P10. We scored the birds from the images in a simplified classification of
1. white underside of P10 not contrasting with underwing coverts, and
2. 'shaded' underside of P10, contrastingly darker than underwing coverts.
We realise such scoring has to be done very carefully (caveat of scoring from one single image) and we keep in mind the difficulties of changing grey-tone depending on observation angle as indicated above. This scoring is merely done to get a general idea of the magnitude of number of birds classified as showing white underside. Ideally, more work with larger sample sizes should be done on the breeding grounds, based on a strict classification to allow comparison with other populations.

Above 2 images: heuglini adult, March 2011, Ashdod, Israel. Picture: Amir Ben Dov. Same bird in both images, scored "shaded base" on underside on P10, contrasting with underwing coverts. (click image for link). Illustrative bird to show the effect of light conditions and observer's angle on the silvery white tongue on underside of P10.

Above: heuglini adult, November 2010, Ashdod, Israel. Picture: Amir Ben Dov. Scored "shaded base" on underside on P10. (click image for link). Impression of different tones in left and right wing, regarding underside of P10.

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below: some example heuglini scored "white base" on underside of P10, as well as several graellsii showing pale bases (however, noticeable slight contrast in some birds).